ob THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 



Thus in the male the first and the second somites bear the remarkable male 

 sperm conductors in Avhich the endopodites greatly exceed the exopodites 

 or else form the only part developed while in the four following jale- 

 opods the larval relation is not much changed in the adult, as the exopodite 

 is as large as the endopodite or, in the sixth pair, larger, and in all these four 

 the function is not sexual but locomotor, or perhaps respiratory. In the female 

 the same state is found in the sixth pair, the first pair are lacking, while the 

 four other pairs have the endopodite much longer than the exopodite and both 

 are used as reproductive organs, as supports for the eggs and larvip. 



Some of the larvjB of the third stage were kept from May 18 to October 2, 

 and some of the moultings and increase in size noted, Init no details of the 

 gradual completion of adult structure were studied. 



The fourth larval stage was reached by a moult after the larva had lived 

 in the third stage twelve to fourteen days and was a little over one month old. 

 The length then increased from 35 mm. to 17 mm. The color was no longer 

 bright Imt dull and inconspicuous, pale grey densely spotted with almost black 

 pigment and scarcely any flesh color though the tips of the chelte were pink. 

 There was a marked transverse band of bluish across the posterior edge of the 

 carapace and the abdomen was much lighter than the thorax. 



The fourth stage had advanced beyond the third in one important par- 

 ticular since now for the first time the ai>pendages of the first abdominal somite 

 were seen in some specimens, which were probal)ly males. These pleopods, how- 

 ever, were as yet but very simple rounded knobs which projected from the 

 sternal ridge of the first somite downward and decidedly inward, toward one 

 another, and were about one-tenth of a millimeter long. 



At the end of June when the larvae had been in the fourth stage about a 

 month they passed into a fifth stage which was nineteen millimeters long 

 and in color red-brown or in some cases decidedly bluish. Kept in running 

 water with water ])lants and tubifex for food and at a tem|)erature as high as 

 21.5° C, they climbed about actively \\])on the jijants or else remained buried 

 in the ooze. 



From some of the larv;e left in a closed aquarium with algal ooze from June 

 1(5 to October 2, there remained one survivor five mouths and a week old that 

 measured 30 mm. in length, 6 mm. in width of thorax, 12 imn. in width of telson- 

 fan, and 2.") uuii. along the antenna. This crayfish having areas for the ends of 

 the oviducts upon the antepenultimate legs was a female, and it had no a])pend- 

 ages upon the first abdominal segment. The color was bright, finely speckled 

 over with brown; the legs lighter; the antenna' dark; the chelse purplish with 

 red and blue spots and there was still a blue transverse band across the iDOste- 

 rior edge of the thorax. The eyes were brown. The shell and flesh were still 

 translucent so that the intestine showed through the dorsal side of the abdomen. 



